45 research outputs found
Carbon nanotubes on partially depassivated n-doped Si(100)-(2x1):H substrates
We present a study on the mechanical configuration and the electronic
properties of semiconducting carbon nanotubes supported by partially
depassivated silicon substrates, as inferred from topographic and spectroscopic
data acquired with a room-temperature ultrahigh vacuum scanning tunneling
microscope and density-functional theory calculations. A mechanical distortion
and doping for semiconducting carbon nanotubes on Si(100)-(2x1):H with
hydrogen-depassivated stripes up to 100 Angstrom wide are ascertained from both
experiment and theory. The results presented here point towards novel and local
functionalities of nanotube-semiconductor interfaces.Comment: 5 pages, 3 Figures, 1 Table. Accepted for publication in Physical
Review
Characterization of nanometer-sized, mechanically exfoliated graphene on the H-passivated Si(100) surface using scanning tunnelling microscopy
We have developed a method for depositing graphene monolayers and bilayers
with minimum lateral dimensions of 2-10 nm by the mechanical exfoliation of
graphite onto the Si(100)-2x1:H surface. Room temperature, ultra-high vacuum
(UHV) tunnelling spectroscopy measurements of nanometer-sized single-layer
graphene reveal a size dependent energy gap ranging from 0.1-1 eV. Furthermore,
the number of graphene layers can be directly determined from scanning
tunnelling microscopy (STM) topographic contours. This atomistic study provides
an experimental basis for probing the electronic structure of nanometer-sized
graphene which can assist the development of graphene-based nanoelectronics.Comment: Accepted for publication in Nanotechnolog
Strain Modulation of Graphene by Nanoscale Substrate Curvatures: A Molecular View
Spatially nonuniform strain is important for engineering the pseudomagnetic
field and band structure of graphene. Despite the wide interest in strain
engineering, there is still a lack of control on device-compatible strain
patterns due to the limited understanding of the structure-strain relationship.
Here, we study the effect of substrate corrugation and curvature on the strain
profiles of graphene via combined experimental and theoretical studies of a
model system: graphene on closely packed SiO2 nanospheres with different
diameters (20-200 nm). Experimentally, via quantitative Raman analysis, we
observe partial adhesion and wrinkle features and find that smaller nanospheres
induce larger tensile strain in graphene, theoretically, molecular dynamics
simulations confirm the same microscopic structure and size dependence of
strain and reveal that a larger strain is caused by a stronger, inhomogeneous
interaction force between smaller nanospheres and graphene. This
molecular-level understanding of the strain mechanism is important for strain
engineering of graphene and other two-dimensional materials.Comment: Nano Letters (2018
Laterally extended atomically precise graphene nanoribbons with improved electrical conductivity for efficient gas sensing
Narrow atomically precise graphene nanoribbons hold great promise for electronic and optoelectronic applications, but the previously demonstrated nanoribbon-based devices typically suffer from low currents and mobilities. In this study, we explored the idea of lateral extension of graphene nanoribbons for improving their electrical conductivity. We started with a conventional chevron graphene nanoribbon, and designed its laterally extended variant. We synthesized these new graphene nanoribbons in solution and found that the lateral extension results in decrease of their electronic bandgap and improvement in the electrical conductivity of nanoribbon-based thin films. These films were employed in gas sensors and an electronic nose system, which showed improved responsivities to low molecular weight alcohols compared to similar sensors based on benchmark graphitic materials, such as graphene and reduced graphene oxide, and a reliable analyte recognition. This study shows the methodology for designing new atomically precise graphene nanoribbons with improved properties, their bottom-up synthesis, characterization, processing and implementation in electronic devices
Scanning Tunneling Microscopy Study and Nanomanipulation of Graphene-Coated Water on Mica
We study interfacial water trapped between a sheet of graphene and a
muscovite (mica) surface using Raman spectroscopy and ultra-high vacuum
scanning tunneling microscopy (UHV-STM) at room temperature. We are able to
image the graphene-water interface with atomic resolution, revealing a layered
network of water trapped underneath the graphene. We identify water layer
numbers with a carbon nanotube height reference. Under normal scanning
conditions, the water structures remain stable. However, at greater electron
energies, we are able to locally manipulate the water using the STM tip.Comment: In press, 5 figures, supplementary information at Nano Letters
websit
Optoelectronic Switching of a Carbon Nanotube Chiral Junction Imaged with Nanometer Spatial Resolution
Imaging and Manipulating Energy Transfer Among Quantum Dots at Individual Dot Resolution
Many processes of
interest in quantum dots involve charge or energy
transfer from one dot to another. Energy transfer in films of quantum
dots as well as between linked quantum dots has been demonstrated
by luminescence shift, and the ultrafast time-dependence of energy
transfer processes has been resolved. Bandgap variation among dots
(energy disorder) and dot separation are known to play an important
role in how energy diffuses. Thus, it would be very useful if energy
transfer could be visualized directly on a dot-by-dot basis among
small clusters or within films of quantum dots. To that effect, we
report single molecule optical absorption detected by scanning tunneling
microscopy (SMA-STM) to image energy pooling from donor into acceptor
dots on a dot-by-dot basis. We show that we can manipulate groups
of quantum dots by pruning away the dominant acceptor dot, and switching
the energy transfer path to a different acceptor dot. Our experimental
data agrees well with a simple Monte Carlo lattice model of energy
transfer, similar to models in the literature, in which excitation
energy is transferred preferentially from dots with a larger bandgap
to dots with a smaller bandgap